EPSRC SUE Waste Consortium

The UK in common with many other countries faces major challenges in achieving sustainability in waste management. The National Waste Strategy (DEFRA, 2000) and the EU Landfill directive have set ambitious targets and deadlines for diversion and recycling of materials currently considered as wastes. More broadly, the prudent use of raw materials is fundamental to sustainable development, and is a key requirement of UK government policy in this area (DETR, 1999). Sustainability will not be achieved without a step change in the efficiency of resource use, however, and this in turn depends on radical re-thinking of definitions for and approaches to waste (PIU, 2001). The proposed research thus addresses major user challenges facing the UK: i) In the short to medium term, to develop techniques and technologies that will allow us to meet the requirements of current and impending legislation, without massive investment in infrastructure and commitment to systems that are too inflexible to respond to changing needs. ii) In the medium to longer term, to achieve a full understanding of the resource cycle in terms of materials, energy, environmental and social implications, in order to provide a basis on which technical decisions can be made and to inform future policy-making.

Major research themes

To meet these challenges, the Consortium focuses on four main themes in resource management research that are crucial for realisation of a sustainable urban environment in the 21st century and beyond. Under each theme is a list of project areas, ranging from technologies and concepts for immediate application to those addressing the longer-term basis for integrated sustainable urban resource management.

SUWIC Contribution

Thermal Processes: Appropriate scales and technologies for energy recovery by thermal processing of waste in the urban environment

Objectives

-To identify optimum types, sizes and distribution of urban thermal energy recovery plant using an LCA approach
-To investigate the potential for pyrolysis and gasification plants to provide decentralised power which could link to future energy requirements and changes in infrastructure
-To bring together a database of information on energy from waste options in the urban environment for future planning of recovery

Description and methods

The overall aim of this project is to investigate the relative sustainability of alternative approaches to thermal processing of urban wastes, with a particular focus on recovery of value in the form of energy products from smaller-scale plant integrated into the urban environment. Through application of a general modelling framework, it is intended to link technology development and assessment activities within the Consortium programme through common questions about the contributions that different options may make to meeting various objectives for urban areas.

Assessment strategy

The project will adopt a cradle-to-grave or life cycle approach, with a primary system boundary set at the point at which a material is designated as waste: from that point, collection, transportation, processing, thermal treatment, and residue management processes will be analysed, together with the production of useful energy and/or material products. Across these stages, the project will address the engineering costs and benefits, the environmental emissions implications and the changes in urban development and infrastructure patterns (through which public acceptability is often influenced). This is a large task as the range of activities is great. Much research has already been done in many areas, however, for example through the waste LCA tools developed by the Environment Agency. The innovations are to bring these materials together in a framework of relevance to urban development and focusing on the emerging range of smaller-scale thermal treatment techniques, with associated and diverse ranges of energy products.

The starting points for technologies to be investigated will be conventional large-scale incineration for energy recovery. For alternative approaches, thermal treatment through smaller-scale pyrolysis and gasification plant will be the primary focus. These plants represent a step change in treatment scale, with associated impacts on the urban environment within which they would be sited. Their range of emissions and final energy products are different and it may also be appropriate to consider some combinations of gasification plant with electricity generator (eg small-scale plants with gas turbines or fuel cells; large-scale cogeneration plants with combined gas and steam turbines).

Pyrolysis and gasification are capable of producing liquid and gaseous fuels from a variety of feedstocks, with lower emissions and at significantly smaller economic scale than conventional large-scale incineration. The variety of energy vectors produced opens up potentially valuable markets for both decentralised stationary power and transport. These technologies could enable waste (and waste-biomass) management to link into a future hydrogen economy and urban infrastructure. Given the smaller economic scale of these technologies and their possible fuel flexibility, the prospects for integrating energy recovering with waste segregation, materials recovery and minimisation are much improved, as are the possibilities for co-combustion with biomass residues or crops. These characteristics imply a wide range of potential effects on urban infrastructure and service provision, whose assessment requires an interdisciplinary systems analysis approach. The project will investigate the suitable size(s) of energy recovery plant through a range of assessment criteria applied to specified technology scenarios. For promising options, the project will investigate the economic aspects involved in the construction of a pilot scale facility and will include market assessments focused on the energy products.

The assessment process described above will be based upon engineering knowledge and an experimental programme that will provide information on the performance of the alternative technology options across the individual steps that may be involved: a) waste segregation, b) shredding, c) pyrolysis, d) gasification, e) combustion, f) power generation, g) gas cooling, h) flue gas cleaning, i) liquid and/ or solid effluent disposal. The efficiency, cost, maintainability, operability and emissions of each step are the basic data required. The experimental programme is broadly divided into three stages, to investigate for each treatment approach: i) the suitability of different waste and virgin biomass feedstocks, and thus the implications for the waste stream to be treated; ii) the performance of the thermal treatment processes themselves; iii) the nature of energy products produced, including chars suitable for use in a further combustion or gasification stage.

Towards a sustainable future.

400 million tonnes of waste is produced in the UK each year. 30 million tonnes of solid waste comes from households of which 87% goes to landfill.

Landfill sites are rapidly running out of space and alternative solutions need to be found not only for disposal or reuse of waste material but also to reducing the amount of waste produced.

SUWIC works at the forefront of research towards developing a sustainable future through technology design and development to utilise waste streams, lower emissions and generate heat and power from waste that would otherwise go to landfill.